I asked a question regarding submitting add-ins with custom functions 6 months ago. The conclusion at the moment was an add-in that uses custom functions cannot curren
Update - Custom Functions are now generally available, so you can now submit add-ins that contain custom functions for validation in the store. If submitting an add-in with Custom Functions, please see the validation policies here:
https://docs.microsoft.com/en-us/office/dev/store/validation-policies#15-add-ins-with-excel-custom-functions